(1) Field of the Invention
This invention relates to a transmission apparatus and, more particularly, to a transmission apparatus for controlling the transmission of signals by introducing cables.
(2) Description of the Related Art
Optical communication network technologies are nuclei for building data communication network infrastructure. In recent years it is hoped that more advanced services will be provided in a wider area. Such technologies therefore are being developed at arapidpace toward an information-oriented society.
In addition, key networks with larger capacity have recently been needed because of, for example, an increase in demand for transmission with the spread of the Internet. This leads to a need for a higher device density, larger information transmission capacity, more advanced functions, and the like.
As a result, there is an increase in the number of optical fiber cables introduced. Therefore, problems about, for example, how to introduce optical fiber cables, cable bunchability, the layout of the enclosure (subrack) of a plug-in unit (PIU), being a unit connected to an optical fiber cable with a connector for controlling an interface for sending and receiving optical signals, have been taken up.
FIG. 27 is a schematic view of a conventional optical transmission apparatus which introduces optical fiber cables from the lower portion of the front. A plurality of PIUs are mounted in a subrack 300 of an optical transmission apparatus 500a. Small PIUs 400a are mounted in the left half of the subrack 300, being a double-decker, and large PIUs 400b are mounted in the right half of the subrack 300 (hereinafter both of the PIU 400a and PIU 400b are referred to as PIUs 400).
When a PIU 400 is mounted in the subrack 300, an optical fiber cable connected to a connector inside the PIU 400 is pulled out from a notch made in the lower portion of a surface plate 41. Then optical fiber cables are bunched along ducts d1 and d2 on the subrack 300.
FIG. 28 is a schematic view of the PIU 400. A notch is made in the lower portion of the surface plate 41 of a PIU 400-1 so that an optical fiber cable can be introduced easily from the front of the subrack 300. A connector 42 is located on the front of the PIU 400-1 and is mounted downward so that an optical fiber cable can be connected to it easily.
FIG. 29 is a schematic view of a conventional optical transmission apparatus which introduces optical fiber cables from the upper portion of the front. In an optical transmission apparatus 500b, optical fiber cables pulled out from the PIUs 400 are bunched along a duct d3 located at the top of the front of the subrack 300.
FIG. 30 is a schematic view of the PIU 400. A notch is made in the upper portion of the surface plate 41 of a PIU 400-2. The connector 42 is located on the front of the PIU 400-2 and is mounted upward.
With the conventional optical transmission apparatuses 500a and 500b described above, optical fiber cables are introduced into the PIUs 400 from the lower or upper portion of the front of the subrack 300. With such apparatuses, a user must be able to insert or pull out the PIUs 400 easily by introducing optical fiber cables for himself/herself.
However, placing first priority on an optical fiber cable being introduced smoothly will lead to a layout (arrangement of PIUs) in which an optical fiber cable can be introduced easily into the PIU 400. A flexible structural design therefore cannot be made. Furthermore, the layout of PIUs will be limited by the direction from which an optical fiber cable is introduced. This will lead to complex wirings on a back wiring board (BWB) at the rear of the subrack 300.
Meanwhile, it is assumed that a multiplexing-separating unit for controlling multiplexing and separating, that is to say, for concentrating and multiplexing signals from units or for separating a multiplexed signal and distributing separated signals to each unit is mounted in a subrack.
In this case, if a multiplexing-separating unit is mounted at the end of a subrack, wirings on a BWB which connect the multiplexing-separating unit and signal processing units for processing signals individually will differ significantly in length. Especially with a system for processing high-frequency signals, a problem about such an arrangement is important.
In order to minimize the difference in wiring length, a multiplexing-separating unit must be located in the middle of the subrack. However, some conventional structures have made it impossible to make such a design.
FIGS. 31(A) and 31(B) are views showing problems with the prior arts. FIG. 31(A) shows a case where optical fiber cables are introduced from the lower portion of the front of a subrack and FIG. 31(B) shows a case where optical fiber cables are introduced from the upper and lower portions of the front of a subrack.
In FIGS. 31(A) and 31(B), it is assumed that an optical transmission apparatus has the following structure. The middle portion of the subrack is a double-decker and the small PIUs 400a (multiplexing-separating control unit) can be inserted into the upper and lower tiers. The large PIUs 400b (signal processing unit) are mounted in the left and right portions of the subrack.
In the case of FIG. 31(A), if the small PIUs 400a (an optical fiber cable is pulled out from the lower portion of the surface plate of each PIU) are mounted in the middle portion of the subrack, optical fiber cables pulled out from the PIUs 400a mounted in the upper tier of the middle portion of the subrack will extend through a space outside the large PIU 400b mounted in the left portion. This will make it impossible to insert or pull out the large PIU 400b freely.
In the case of FIG. 31(B), ducts are located at the top and bottom of the front of the subrack in which PIUs 400a-2, a PIU 400b-2, PIUs 400a-1, and a PIU 400b-1 are mounted. An optical fiber cable is pulled out from the upper portion of the surface plate of each of the PIUs 400a-2 and PIU 400b-2. On the other hand, an optical fiber cable is pulled out from the lower portion of the surface plate of each of the PIUs 400a-1 and PIU 400b-1. In this case, the problem which arises in FIG. 31(A) can be solved, but two types of PIUs (a PIU of one type introduces an optical fiber cable from the upper portion of its front and a PIU of the other type introduces an optical fiber cable from the lower portion of its front) with the same functions must be designed. A user must also keep these two types of PIUs with the same functions in stock. This will lead to extremely low efficiency in design, maintenance, and purchase.
In order to address such problems, the present invention was made. In other words, an object of the present invention is to provide a transmission apparatus having a flexible external cable introduction structure for controlling the transmission of signals efficiently.
In order to achieve the above object, a transmission apparatus for controlling signal transmission by introducing cables is provided. This transmission apparatus comprises transmission units each including a sub-printed circuit board on which a cable connector for introducing the cable from the outside is fixed and a main printed circuit board with a guide rail along which the sub-printed circuit board can be inserted reversely to change the direction from which the cable is introduced at the time of the sub-printed circuit board being housed and an enclosure with ducts for bunching the cables in which the transmission units are mounted.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.